The operating principle is that air will act as oxidizer to a aerosol of fuel in a volume of atmosphere near the ground when the fuel is dispersed and ignited with precision. In military ordnance a conventional primary explosive ruptures the weapon container and disperses the fuel, and secondary explosive(s) detonate the mixture after a precise delay, producing overpressures up to 30 kg/cm2 in a blast wave that moves at 3 km/sec and and a few dozen microseconds later reverses to a brief hard vacuum.

In an accidental, low-efficiency civilian instance, someone lights a cigarette inside a silo full of fine wheat chaff, or natural gas from a leaking cooking bottle in an apartment floods its way down to a candle on the floor below.

Military FAE's are twelve to sixteen times more powerful than conventional munitions against targets with large surface areas such as frame buildings, bunkers and vehicle shelters. They are more effective against fortifications not only because overpressures from FAE's travel through such fortifications more pervasively than the blast from point-source explosions, but because the major detonation can be delayed until the fuel aerosol itself has saturated the target. Several can also be exploded in near-simultaneous ripples that reinforce each other's blast waves. This makes fuel-air explosives a nearly unparalleled destructive force, and an effective if brutal alternative to the vicious room-by-room, block-by-block infantry tactics that are the traditional paradigm for urban operations.

From www.igc.com:

In urban settings it is very difficult to limit the effect of this weapon to combatants, and the nature of FAE explosions makes it virtually impossible for civilians to take shelter from their destructive effect.

The (blast) kill mechanism against living targets is unique, and unpleasant... What kills is the pressure wave, and more importantly, the subsequent rarefaction (vacuum), which ruptures the lungs. If the fuel deflagrates but does not detonate, victims will be severely burned and will probably also inhale the burning fuel. Since the most common FAE fuels, ethylene oxide and propylene oxide, are highly toxic, undetonated FAE should prove as lethal to personnel caught within the cloud as most chemical agents.

I was noding a response to this and it growed. It is Armistice Day and I feel an obligation not to squeam, for the sake of those who had and have no choice but pro patria mori, and for those who chose anyway.

The largest air-deliverable conventional weapon in the world is a Fuel-Air Explosive. The BLU-82 was developed by the USAF during the Vietnam War. For what, exactly, only God and the propellerheads in some basement in the Pentagon know.

They used one of these in the Gulf War. It was a distraction tactic to misdirect the Iraqis from the armored Hail Mary that would constitute the ground war. For 3 days, psyops dropped leaflets on the Iraqi positions that roughly read (in Arabic):
BIG BLU is coming! On Thursday, the largest conventional airdropped bomb in the world, the BLU-82, will be dropped on your position.

I guess the intent was to hurl the golden apple of discord amongst the ranks of the Republican Guard, and send a misleading message to the Iraqi central command. When the bomb was dropped, right on schedule, a British SAS recon team broke radio silence to report: